How to log attempts to connect as a locked user account

I want to design poor man's auditing for one single case: My user
accounts are locked, and I want to log the connection attempts. But
since there is no BEFORE LOGON ON DATABASE trigger (for rather obvious
reasons).

(Background info: Decommissioning of a test database: I want to find
ancient jobs or autistic developers that don't complain, before dropping
the storage there.)